1. Field of the Invention
The present invention relates to a magnetic separating purification apparatus, particularly to a purification apparatus which can continuously separate and remove magnetic substances easily.
2. Description of the Related Art
As an example of a technique for removing pollutants from water to purify the water, there is provided a magnetic separation technique. As the technique for use in a continuous water purification apparatus for seas, rivers, reservoirs or the like, Japanese Patent Unexamined Publication No. 59-371 discloses a magnetic separation apparatus using a high-gradient magnetic filter. The thus apparatus will be described later with reference to FIG. 11.
In such an apparatus, in preparation for a magnetic separation process, after raw water to be treated is taken, for example, iron tetroxide or another magnetic powder and alumina sulfate, polychlorinated aluminum or another flocculant are applied to the raw water and stirred. Solid floating substances, algae, fungi and microorganisms in the raw water are combined by the flocculant with magnetic flocks to form multiple colloidal magnetic aggregate or substances. When passing a magnetic separating portion, these magnetic substances are drawn by the separating portion and separated from the raw water. In the magnetic separating portion, the magnetic substances in the raw water are caught by a large magnetic force on a high-gradient filter surface, and purified water is discharged as treated water.
In the prior art, the magnetic substances are caught by the filter. Therefore, when a certain or more amount of magnetic substances are caught, a capture force given by means of magnetic force is weakened due to piling of the magnetic substances on the filter. Then, to recover the performance of magnetic separation, the filter is subjected to backwashing, and the magnetic substances caught on the filter surface are washed and removed. At this time, the magnetic force for adsorbing the magnetic substances is eliminated or lowered to enhance the washing efficiency.
However, in the above conventional apparatus, it is difficult to perform the magnetic separation during the backwashing. Also, it is not easy to wash the magnetic substances out of fine portions of the high-gradient magnetic filter. It takes much time to perform backwashing while stopping the magnetic separating operation, which largely deteriorates the efficiency of the purification process. Thus, in the conventional apparatus, the problem that the backwashing lowers the efficiency of the entire process has not been considered.
Also, the following problem has not been considered. If time interval between the backwashing operations is lengthened so as to increase the purification efficiency, a space has to be enlarged for accumulating and storing the caught magnetic substances in the vicinity of the filter. Since the volume of the magnetic separating portion is enlarged, an electromagnet is enlarged in size or has to generate a large magnetic force. Therefore, electric power for operating the large-sized electromagnet is increased.
As aforementioned, in the prior art of catching magnetic bodies with the filter, the filter needs to be subjected to backwashing to remove the caught magnetic bodies from the filter. Therefore, the filter cannot be disposed in a backwashing direction. It is difficult to provide plural magnetic separating portions in one apparatus. A flow rate to be treated has a limitation.